Thursday, July 21, 2011

Conduit to trunking connections

I attach here a few pictures showing the connections between electrical conduits and trunking. Some few weeks ago a reader left a message on one of my blogs asking how to connect a branch conduit to a steel trunking. So these pictures should be self-explanatory enough how to make the connection.

Picture 1 – Electrical and mechanical services above the ceiling of an office building

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The above picture shows some of the services inside the ceiling space of and office building.

Here you can see some conduit and trunking works. For large office floor space, conduit alone is usually not enough to contain the wiring cables from the floor distribution panels to the lighting and power points.

However, it not practical and a sheer waste to use trunking up to a final circuit point, a light point for example.

A lighting point needs only three wires of 1.0 mm.sq. or 1.5 mm.sq. to make a complete wiring. This does not need a trunking. It is also difficult to connect a trunking to a lighting fixture.

Therefore, the wiring to the lighting point needs to be routed into a conduit. The best is flexible conduit.

The following two pictures show how a trunking branched into rigid and flexible conduit.

Picture 2 – Conduit branching into rigid metal conduits

The above shows two branches into rigid steel conduits. One using a circular draw box as an adapter, and the other is connected directly to the metal trunking without any drawbox.

Either one is fine, but if you have a number of circuits to be run into the branch conduit, then using the draw box might me more preferable. It would ease the work of drawing the wire.

If the tap off needs to supply only one lighting point, then you can save one draw box by connecting the trunking to the conduit directly.

Another reason for using the draw box is when the conduit do not connect to the trunking at 90 degree angle to the connected side. In that case, you definitely need the draw box.

In any case, the conduit and trunking works is a skilled tradesman’s work. Often many aspects of the actual installation tasks require some creativity and experience to do it properly at a reasonable cost.

If some tradesman have a long list of better ways to do this connection than the ones that I show in this post, then by all means follow him.

What I show here are those that are usually practiced locally here.

Picture 3 – Another two connections at the same location

One more important aspect of the connection between the electrical trunking and conduit is how exactly to fix the two pieces of electrical container.

It is not visible how it is done from the above three pictures. I also keep forgetting to open up an electrical trunking and take the picture of the connection inside the electrical trunking.

The third piece of the component that makes up the connection is only visible from inside the trunking which I presently do not have any picture.

However, there is one place where it is easier to see that third component. It is at the connection between a rigid electrical conduit and the concealed metal box of a socket out or a wall mounted light switch. The pictures below show this quite clearly.

Picture 4 – Connection between rigid electrical conduit and a concealed metal box

I have labeled the relevant components so you can see clearly what are involved in the connection between the conduit and the concealed box.

The “copper bush” is the component that I wish to show you. It is this same component that is used between conduits and trunking. When the conduit and trunking are made of metal materials, the “bush” is usually of copper material. This provides a good electrical connection between the conduit and the trunking.

On the other hand, if the conduit and trunking are of plastics or PVC materials, which are also quite commonly used in certain types of electrical installations, then the “bush” would be made of plastic or PVC.

The functions of the copper bush are three fold: one is to keep the connection firm and strong. The second is to provide a smooth finished that would not injure the insulation of wiring cables when they are drawn through the joint or connection. Lastly it serves to provide a good electrical continuity between the trunking and the conduit.

The following three more pictures give more view of the copper bush.

Picture 5 – A closer view of the copper bush in Picture 4

Picture 6 – Copper bush at another lighting switch with some wiring being installed

Here I use a picture that has some wiring already drawn in to show you how wiring cable can be damaged if the area around the connection is not smooth enough.

Copyright Conduit to trunking connections


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-JoJo- said...

looking forward for more knowledge

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